A Hong Kong court has found leaders of the 2014 "Occupy" civil disobedience movement guilty of public nuisance charges during the mass protests, in a landmark verdict that comes as the China-ruled city's freedoms come under strain.

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Human Rights Watch said the verdict had a "chilling" effect on free speech

Scores of supporters clapped in support of the nine defendants including a law professor, two members of the Legislative Council of Hong Kong and former student activists, after the judge delivered his verdict following a trial that critics say highlights shrinking political freedoms in the former British colony.

Three of the defendants accused of playing a leading role mobilising supporters during the 79-day street occupations in 2014 — Benny Tai, 54, Chan Kin-man, 60, and retired pastor Chu Yiu-ming, 75 — were found guilty of conspiracy to commit public nuisance.

Tai and Chan were also found guilty of incitement to commit public nuisance. They appeared calm after the verdict was delivered, and Chan bowed to supporters, applauding them outside the court.

The trio had pleaded not guilty to all charges, which each carry a maximum seven years' jail.

In a summary of his judgement, Justice Johnny Chan noted that while the concept of civil disobedience is "recognised in Hong Kong", it was not a defence to a criminal charge.

"The offence of conspiracy to cause a public nuisance does not have the undesirable effect of curtailing or suppressing civil disobedience at its formation stage or suppressing human rights as the defendants contended," the summary read.

The six other defendants include pro-democracy Legislative Councillors Tanya Chan and Shiu Ka-chun, two former student leaders Eason Chung and Tommy Cheung, activist Raphael Wong, and veteran democrat Lee Wing-tat, were also found guilty of at least one public nuisance charge.

Beijing's 'tightening grip' on Hong Kong

Since the city returned from British to Chinese rule in 1997, critics say China has reneged on its commitment to maintain Hong Kong's high degree of autonomy and freedoms under a co-called "one country, two systems" arrangement.

Chris Patten, Hong Kong's last British governor, called the verdict "appallingly divisive" and a "vengeful pursuit" of past political events.

In Beijing, Foreign Ministry spokesman Lu Kang told a regular news briefing that criticising the verdict as indicative of shrinking freedoms in the city was "illogical and baseless".

The central government supported the move "to punish, according to law, the main … plotters of the illegal Occupy [movement]", he said.

In the nearly five years since the Occupy protests, democracy activists, diplomats and business leaders have expressed grave concern over what they described as Beijing's tightening grip on the city's freedoms.

Pro-democracy Legislative Councillors have been kicked out of the Legislative Council, a pro-independence party banned, and democracy advocates barred from contesting local elections.

Maya Wang, senior China researcher at Human Rights Watch, said the verdict had a "chilling" effect on free speech.

"Hong Kong courts, by labelling peaceful protests in pursuit of rights as public nuisance, are sending a terrible message that will likely embolden the Government to prosecute more peaceful activists, further chilling free expression in Hong Kong," she said.

Umbrella movement

The nine defendants were accused of inciting and mobilising protesters during the demonstrations that sought to pressure Beijing to allow full democracy.

Hundreds of thousands of people blocked major roads in several parts of the global financial hub for 79 straight days in late 2014, in one of the boldest populist challenges against Beijing in decades.

The demonstrators were finally cleared away by police, having won no democratic concessions from the Government.

David Leung, the director of public prosecutions, had earlier argued that Tai, Chan and Chu were the main conspirators who had begun planning the protests a year in advance.

He also said the protests had caused "unreasonable" public disruptions over nearly three months.

A public opinion poll by the Chinese University of Hong Kong that was cited in court found that of some 1,200 protesters polled during the demonstrations, 87 per cent said they had participated to "protect Hong Kong's liberty".

The 268 page judgement noted, however, that: "It is naive to suggest that a concession to introduce the form of universal suffrage … could be made by the Government overnight with a click of the fingers, it is equally naive to suggest a mass protest of tens of thousands of people could be dispersed overnight even if a positive response were to come from the authorities."